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Second level
Third level
Fourth level
Fifth level
Fleming Diode
De Forest Triode
Senveral layers in ionosphere
In densest layer (F-layer) electron concentration up to 10^12 e- / m3
(compare with metals of 10^28 /m3)
On December 12th 1901 Marconi recieves signal sent from Cornwall  in  St Johns, New Foundland, Canada. receives the signal which is send from Poldhu, Cornwall England.
1920 Marconi broadcast from chelmsford, essex station
Programming included opera
1922 Post office licensed 2LO (London) & 2MT (chelmsford)
First eye evolved 540 million years ago as patch of photoreceptor cells
patch gives light/dark (move into dark to avoid detection)
cells line pit č limited directionality
pit deepens č pinhole camera
cover entrance for protection
shape cover č lens
Impressive imaging device
Sensitivity down to single photon (fully dark adjusted)
Dynamic range 1,000,000:1
Rods, highly sensitive, spread across retina.
Highest sensitivity away from centre of vision. View faint objects in peripheral vision.
Cones, RGB sensitive, concentrated in fovea.
Photoreceptors in eye have:
logarithmic response
built-in edge & movement enhancing processing
Static dynamic range of retina 100:1 – adjusts to low light levels chemically over 30minutes timeframe.
Optic nerve takes signals to visual cortex via optic tract
100:1 data reduction
Image from
Response of red (r), green (g) and blue (b) cones to light
Sensitive from 380-700nm
Image from Radiant Imaging colour calculator
photoconductivity of the element selenium: Willoughby Smith in 1873
Scanning disk by Paul Nipkow in 1884.
The two inventions were first joined for practical use in the electronic transmission of still pictures and photographs, and by the first decade of the 20th century halftone photographs were being transmitted by telegraph and telephone lines as a newspaper service.
Tried to create diamonds by heating graphite and shorted out Glasgow's electricity supply.
Baird perfected a glass razor; it was completely rust resistant, but it shattered.
Inspired by pneumatic tyres he had a go at pneumatic shoes, but his prototype contained semi-inflated balloons which burst.
He also invented a thermal undersock, which was actually a mild success.
Philo Taylor Farnsworth (August 19, 1906March 11, 1971)
Evolved from Crookes tube
Heater boils off electrons from cathode
electrons drawn from cathode towards 1st anode
through hole in anode forming beam
through 2nd anode
focussed into narrow beam be focussing coils
impinge upon fluorescent screen to produce light
control grid controls current in beam č light output
beam deflected across screen by deflection coils
Image from encyclopaedia Brittanica
Light form image produces electrons in photocathode
electrons drawn to target screen – knock off electrons from screen by secondary emission
land on front face of thin glass target
induce positive charge on rear of glass depending on brightness of image
Image of scene now in +ve electrostatic charge on rear of screen
Scanning beam from cathode arranged to ‘just’ reach target before being drawn back to electron multiplier next to cathode.
Electron multiplier ‘avalanche muultiplication’ 1 eletron in, 1000s outs
electrons in beam neutralise +ve charge on rear of plate
bright point in image č high +ve charge on plate č low return current
dark point on image č low +ve charge on plate č high return current